1. Field of the Invention
The subject invention relates to compositions which inhibit the corrosion caused by CO.sub.2 and H.sub.2 S in the transport and storage of crude oils, which are generally water-in-oil, in particular salt-water-in-oil emulsions. The corrosion inhibitors are mixtures of certain imidazoline or tetrahydropyrimidine derivatives, precursors thereof, or their complexes with sulfur and certain maleinamidic acids.
2. Description of the Prior Art
The common practice when oil is piped, transported, and stored is to inject a solution or dispersion of corrosion inhibitors into the oil so that a protective layer is formed on the surface of metal parts coming in contact with the oil.
German Published Application No. 28 46 977 discloses corrosion inhibitors for these purposes which are comprised of an imidazoline salt, an oil-soluble solvent for the imidazoline salt, and a hydrocarbon oil.
However, it has been found that particularly with salt-water-in-oil emulsions (henceforth shortened to "W/O emulsions") the imidazoline salts described in the above reference still do not sufficiently suppress corrosion due to H.sub.2 S and CO.sub.2. Furthermore, the use of the imidazolines is complicated here by the fact that they must be used with specific solvents and a hydrocarbon oil; thus, they are expensive to use.
European Patent Application No. 82101713.4, which is a counterpart of German Application P 31 09 827.4, discloses an inhibitor against corrosion caused by CO.sub.2 and H.sub.2 S in water-in-oil emulsions consisting of the reaction product of
(A) compounds or their salts having formula (i) ##STR1## or precursors having formula (ii) ##STR2## where R.sup.1 =C.sub.6 - to C.sub.22 -alkyl or alkenyl
X=--OH, --NH.sub.2 or ##STR3## R.sup.2 =C.sub.4 - to C.sub.18 -alkyl, n=2 and PA1 (A) a compound selected from the group consisting of PA1 (i) a compound or salt thereof having the formula ##STR4## (ii) a precursor of (i) having the formula ##STR5## in which R.sup.1 =C.sub.6 to C.sub.22 alkyl or alkenyl;
(B) elementary sulfur.
These inhibitors are generally effective, but their preparation is not energy-efficient due to the necessary incorporation of sulfur, and their effectiveness as inhibitors is not optimum in all cases.
Thus, there is a need to develop improved inhibitors which will provide increased protection against corrosion caused by H.sub.2 S and CO.sub.2, primarily in salt-water-in-oil emulsions.